Young women ages 16-24 report the highest rates of intimate partner violence (IPV) and over three quarters of women experiencing sexually assault (SA) for the first time do so before the age of 25. Despite the high prevalence of IPV/SA reported among adolescent females and substantial reports of perpetration by young males, effective prevention programs to stop perpetration of IPV/SA are limited. Male athletes are an important target for prevention efforts given their higher rates of IPV/SA perpetration compared to non-athlete peers as well as their social influence among their peers. The proposed cluster-randomized school-based investigation will examine the effectiveness of a program for the primary prevention of IPV/SA. "Coaching Boys into Men" (CBIM) is a social norms and social cognitive theory-based program intended to alter norms that foster IPV/SA perpetration, promote bystander intervention, and reduce IPV/SA perpetration by engaging athletic coaches as positive role models to deliver violence prevention scripts and tools to high school age male athletes. The CBIM model has been developed and piloted by a team of experts and stakeholders coordinated by the Family Violence Prevention Fund and the Waitt Institute for Violence Prevention. Trained high school coaches talk to their male athletes about 1) what constitutes disrespectful and harmful vs. respectful relationship behaviors, 2) promoting more gender-equitable attitudes, and 3) modeling bystander intervention when disrespectful male behaviors toward women and girls are witnessed. The hypothesized outcomes for male athletes include a) an increase in knowledge of what constitutes abusive behaviors, b) more gender-equitable attitudes, c) an increase in intentions and reports of bystander intervention regarding IPV/SA, and through these three intermediate outcomes, d) a decrease in perpetration of IPV/SA among adolescent male athletes. Coaches receive a sixty-minute training session and bi-weekly support sessions to administer the intervention to their athletes via 11 lessons across a sport 'season'(i.e., fall, winter, or spring). Building on promising results from pilot evaluation of CBIM, the current investigation entails evaluation of the intervention in 14 urban high schools randomized either to receive the CBIM program (i.e., intervention schools, n=7) or to a control condition (n=7 schools). Baseline computer-assisted surveys will be collected for all intervention and control site student athletes entering grades 9 through 11 at the start of each of three sports seasons across Year 1 (Time 1). Follow up computer-based surveys will be collected for these same athletes at the end of their first sports season (Time 2). All participating athletes will be re-surveyed 12 months after Time 2 to examine the longer term effects of the CBIM intervention (Time 3;N of athletes completing all 3 waves of data collection = 1500). Primary assessment of intervention effects will be based on intent-to-treat estimates, utilizing generalized linear mixed models to account for clustering arising from school randomization. All project partners will participate in project implementation, interpretation of results, and dissemination of findings. The proposed cluster-randomized school-based project will examine the effectiveness of a program for the primary prevention of intimate partner violence (IPV) and sexual assault (SA). "Coaching Boys into Men" (CBIM) is a social norms and social cognitive theory-based program that is intended to alter norms that foster IPV/SA perpetration, promote bystander intervention, and reduce IPV/SA perpetration by engaging coaches as positive role models to deliver violence prevention scripts and tools to high school age male athletes. 14 large urban high schools will be randomized to either intervention or control conditions, with male athletes grades 9- 11 (final N= 1500) completing surveys at baseline (Time 1), at end of their sports season (Time 2), and 12 months after the end of their first Year 1 sports season (Time 3) to assess changes in athletes'IPV/SA related knowledge, attitudes, and behaviors.